KR20140114750A - Ferroelectric thin film-forming sol-gel solution - Google Patents

Abstract

A sol-gel solution for forming a ferroelectric thin film includes: a PZT-based compound; a polymer compound to adjust the viscosity and including polyvinyl pyrrolidone; and an organic dopant including N-methyl pyrrolidone, wherein, the amount of the PZT-based compound is greater than or equal to 17 mass % in terms of oxides, the molar ratio (PZT-based compound: polyvinyl pyrrolidone) of the PZT-based compound to the polyvinyl pyrrolidone is 1:0.1 to 1:0.5 in terms of monomers, and the amount of the organic dopant including N-methyl pyrrolidone in the sol-gel solution is 3 mass % to 13 mass %.

Description

{FERROELECTRIC THIN FILM-FORMING SOL-GEL SOLUTION}

The present invention relates to a sol-gel solution for forming a ferroelectric thin film. More particularly, the present invention relates to a ferroelectric thin film forming method in which even when a single layer of a sol-gel solution for forming a ferroelectric thin film applied by a chemical solution deposition (CSD) method has a thickness exceeding several hundreds nm, To a sol-gel solution for forming a ferroelectric thin film which is cracked after sintering and which can obtain a dense ferroelectric thin film.

The present application claims priority to Japanese Patent Application No. 2013-056229 filed on March 19, 2013, the contents of which are incorporated herein by reference.

In the conventional CSD method, for example, in the sol-gel method, when a PZT ferroelectric thin film (referred to as a "PZT film") is formed on a substrate, a sol-gel solution for forming a PZT ferroelectric thin film It has been considered that a film thickness of about 100 nm is the limit when one layer of coating is formed. This is because, when the film having a thickness exceeding 100 nm is calcined and fired, a tensile stress generated in the PZT film occurs unevenly in the same film, and cracks often occur in the same film. Therefore, in order to obtain a PZT film having a few 탆 thick film, it is necessary to repeat the calcining and firing while applying one layer several times and applying it several times. However, with this method, the production efficiency is lowered and the film forming cost is increased.

In view of the above problems, there has been proposed a sol-gel liquid in which propylene glycol is used as an organic solvent used for preparing a sol-gel liquid and a thick film having a thickness of 200 nm or more per layer of the sol-gel solution is applied (for example, , Japanese Laid-Open Patent Publication No. 2001-261338 (Claim 1, paragraphs [0016] to [0024], Table 1)). Further, a method has been proposed in which a polymer is added to a sol-gel solution at a high concentration to alleviate a tensile stress generated during the film formation, thereby thickening one layer obtained by applying the sol-gel solution (see, for example, J Sol-Gel Sci Technol (2008) 47: 316-325).

In addition, Japanese Patent Application Laid-Open No. 2001-521976 discloses the use of N-methylpyrrolidone as a solvent of an ink composition for ink-jet printing obtained by dispersing a core / shell polymer binder and a ferrite powder (for example, , Paragraphs [0013] and [0188]). However, the composition disclosed in Japanese Laid-Open Patent Publication No. 2001-521976 is a composition for ink-jet printing, and the smear fastness of the core / shell polymer binder is improved by the above-mentioned core / shell polymer binder. That is, the composition disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2001-521976 is completely different from the sol-gel liquid of the present invention described below in constitution and purpose. The composition disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2001-521976 is a composition comprising a dispersion obtained by dispersing ferrite powder in a solvent. The composition is completely composed of the sol-gel composition of the present invention using a metal alkoxide or the like as a raw material It is different.

The inventors of the present invention have found that it is difficult to produce a PZT film having a cracked, dense film structure and sufficient characteristics for practical use even using the sol-gel solution proposed above.

It is an object of the present invention to provide a PZT ferroelectric thin film forming sol which can crack and form a dense PZT film after firing and firing even when one layer formed by applying the sol-gel solution has a layer thickness exceeding several hundred nm Thereby providing the gel solution.

According to a first aspect of the present invention, there is provided a ferroelectric thin film-forming sol-gel solution, wherein the sol-gel solution contains a PZT compound, a viscosity-adjusting polymer compound containing polyvinylpyrrolidone, Dopants,

Wherein the PZT compound is contained in an amount of 17 mass% or more in terms of an oxide, the molar ratio of the polyvinylpyrrolidone to the PZT compound is in a ratio of PZT compound: polyvinylpyrrolidone = 1: 0.1 to 0.5 in terms of monomer, Methylpyrrolidone is contained in an amount of 3% by mass to 13% by mass of the sol-gel solution.

The second aspect of the present invention is the invention based on the first aspect and is a sol-gel solution for forming a ferroelectric thin film described in the first aspect, wherein the k value of the polyvinylpyrrolidone is in the range of 15 to 90 Do.

Here, the value k is a value calculated by the following Fikentscher's equation using a relative viscosity value (25 DEG C) measured by a capillary viscometer, which is a viscous characteristic value correlated with the molecular weight.

k value = (1.5 log? rel-1) / (0.15 + 0.003 c)

+ (300 clog? Rel + (c + 1.5 clog? Rel) ² ) ^{1/2 / (} 0.15 c + 0.003 c ² )

relative viscosity (25 DEG C) of polyvinylpyrrolidone aqueous solution to water (c); polyvinylpyrrolidone concentration (wt%) in aqueous polyvinylpyrrolidone solution)

A third aspect of the present invention is a method for forming a ferroelectric thin film using a sol-gel liquid for forming a ferroelectric thin film based on the first or second aspect.

The sol-gel solution for forming a ferroelectric thin film according to the first aspect of the present invention comprises a PZT-based compound, a viscosity-adjusting polymer compound containing polyvinylpyrrolidone, and an organic dopant containing N-methylpyrrolidone as a polar solvent and,

Wherein the PZT compound is contained in an amount of 17 mass% or more in terms of an oxide, the molar ratio of the polyvinylpyrrolidone to the PZT compound is in a ratio of PZT compound: polyvinylpyrrolidone = 1: 0.1 to 0.5 in terms of monomer, Methylpyrrolidone is contained in an amount of 3% by mass to 13% by mass of the sol-gel solution. In the present invention, because of the constitution of the sol-gel solution, it is possible to appropriately form a gap in the membrane during the drying process and effectively remove the gas or the like accompanying decomposition from the membrane, so that the sol-gel solution is used as a PZT ferroelectric thin film It is possible to produce a PZT film having a cracked, dense film and having sufficient characteristics for practical use.

In the sol-gel liquid for forming a ferroelectric thin film according to the second aspect of the present invention, as the invention based on the first aspect, the k value of the polyvinylpyrrolidone is within the range of 15 to 90. Therefore, the sol- When used in the production of a ferroelectric thin film, a better PZT film having a cracked, dense film structure and sufficient practical properties can be produced.

According to the method for forming a ferroelectric thin film of the third aspect of the present invention, a better PZT film having a cracked, dense film structure and sufficient practical characteristics can be produced.

A sol-gel solution for forming a ferroelectric thin film according to the present embodiment will be described below as a representative example of a PZT-based ferroelectric thin film-forming sol-gel solution (hereinafter referred to as " PZT sol-gel solution "

The PZT sol-gel liquid according to this embodiment contains a PZT compound, a viscosity-adjusting polymer compound containing polyvinylpyrrolidone (PVP), and an organic dopant containing N-methylpyrrolidone, and the PZT system Wherein the molar ratio of the polyvinylpyrrolidone to the PZT-based compound is in a range of 1: 0.1 to 0.5, the PZT-based compound is polyvinylpyrrolidone in terms of monomer, Methyl pyrrolidone is contained in an amount of 3% by mass to 13% by mass of the sol-gel solution.

First, a description will be given of a PZT compound, a viscosity-adjusting polymer compound containing polyvinylpyrrolidone, and an organic dopant containing N-methylpyrrolidone, which are basic contents of the PZT sol-gel solution of the present embodiment.

The PZT compound includes compounds other than PZT such as PLZT, PMnZT, and PNbZT. The raw material of the PZT compound is preferably a compound in which an organic group is bonded to each metal element of Pb, La, Zr and Ti via an oxygen or nitrogen atom. For example, metal alkoxide, metal diol complex, metal triol complex, metal carboxylate, metal? -Diketonate complex, metal? -Diketo ester complex, metal? -Iminocate complex, and metal amino complex , And at least one selected from the group consisting of Particularly preferred compounds are metal alkoxides, partial hydrolyzates thereof, and organic acid salts.

Of these, the Pb compound and the La compound include an acetate salt (lead acetate: Pb (OAc) ₂ , lanthanum acetate: La (OAc) ₃ ), lead diisopropoxide: Pb (OiPr) ₂ , lanthanum triisopropoxide And side: La (OiPr) ₃ . Examples of the Ti compound include titanium tetraethoxide: Ti (OEt) ₄ , titanium tetraisopropoxide: Ti (OiPr) ₄ , titanium tetra n-butoxide: Ti (OiBu) ₄ , titanium tetraisobutoxide: Ti (OiBu) ₄ , titanium tetra-t-butoxide: Ti (OtBu) ₄ and titanium dimethoxydiisopropoxide: Ti (OMe) ₂ (OiPr) ₂ . As the Zr compound, the same alkoxide as the Ti compound is preferable. The metal alkoxide may be used as it is, but the partial hydrolyzate may be used to promote decomposition.

The PZT-based compound in the PZT sol-gel solution is obtained by a method for preparing a raw material solution of a PZT sol-gel solution containing a PZT-based compound described later using the above-mentioned raw materials.

In the viscosity-adjusting polymer compound containing polyvinylpyrrolidone, polyvinylpyrrolidone (PVP) is a compound capable of adjusting the liquid viscosity. More specifically, the relative viscosity can be determined and adjusted by the above-described k value. Here, the k value is a value calculated by applying the relative viscosity value (25 DEG C) measured by the capillary viscometer to the following Fikentscher's equation, which is a viscous characteristic value correlated to the molecular weight.

k value = (1.5 log? rel-1) / (0.15 + 0.003 c)

+ (300 clog? Rel + (c + 1.5 clog? Rel) ² ) ^{1/2 / (} 0.15 c + 0.003 c ² )

Represents the relative viscosity (25 DEG C) of the aqueous solution of polyvinylpyrrolidone with respect to water, and " c " represents the concentration of polyvinylpyrrolidone (wt%) in the aqueous solution of polyvinylpyrrolidone .

In the present embodiment, polyvinyl pyrrolidone having a k value in the range of 15 to 90 is preferable. When the value of k is less than 15, there is a problem because it is insufficient to obtain a sufficient viscosity for obtaining a thick film. When the value is more than 90, there is a problem that the viscosity is too high and uniform application is difficult. More preferably, the k value is 30 to 45.

As the other polymer compound, polyethylene glycol having a degree of polymerization of 100 to 1000 may be used. If the degree of polymerization is less than 100, a sufficient viscosity can not be obtained. Thus, there is a problem. When the degree of polymerization is more than 1000, the viscosity is excessively high, which makes it difficult to apply uniformly.

The content of polyvinylpyrrolidone in 100 mass% of the polymer compound is preferably 50 to 100 mass%, more preferably 80 to 100 mass%.

By combining the organic dopant containing N-methylpyrrolidone and the polymer compound containing polyvinylpyrrolidone, one layer by applying the sol-gel solution for the purpose of the present invention can be formed into a layer having a thickness of several hundreds nm It is possible to produce a PZT sol gel liquid which is cracked and can form a dense PZT film after calcination and firing.

The organic dopant preferably further contains an ethanolamine such as monoethanolamine or diethanolamine. These ethanol amines are effective for enhancing the storage stability of the solution to be fed to the metal alkoxide.

In 100 mass% of the organic dopant, the content of N-methylpyrrolidone is preferably 80 to 100 mass%, more preferably 90 to 100 mass%. On the other hand, the content of the ethanolamine is preferably 0 to 30 mass%, more preferably 0 to 20 mass%, in 100 mass% of the organic dopant.

Next, the prescription for the PZT sol-gel solution of the basic inclusion will be described.

First, the PZT compound is contained in an amount of 17 mass% in terms of oxide in the PZT sol-gel solution. If the content is less than 17 mass%, the concentration of the precursor is low and a sufficient film thickness can not be obtained. And preferably 23 mass% or less. If it exceeds 23 mass%, the proportion of the lower alcohol which is a diluent is lowered, which may lead to deterioration of the coating film property and storage stability.

A more preferable content of the PZT compound in the PZT sol gel solution is 17 mass% or more and 28 mass% or less.

Here, oxide conversion refers to the ratio of the metal oxide occupying 100% by mass of the PZT sol-gel solution when it is assumed that all the metal elements contained in the PZT sol-gel solution are oxides.

Next, the molar ratio of the polyvinylpyrrolidone to the PZT-based compound is adjusted to be PZT compound: polyvinylpyrrolidone = 1: 0.1 to 0.5 in terms of the monomer.

Here, the monomer conversion is a value obtained by converting the molecular weight of the polymer with the molecular weight of the monomer constituting the polymer as a reference (1 mole).

This is because when the molar ratio is less than 1: 0.1, sufficient viscosity can not be obtained, stress relaxation can not be performed, and there is a problem of cracking. When the molar ratio is more than 1: 0.5, More preferably, the PZT compound: polyvinylpyrrolidone is 1: 0.2 to 0.45. This is because when the molar ratio is less than 1: 0.2, there is a problem that the width of the process temperature is narrow and cracks are generated well, and when the molar ratio exceeds 1: 0.45, there is a problem that a little void occurs.

And, N-methylpyrrolidone is contained in 3 mass% to 13 mass% in 100 mass% of PZT sol-gel solution. If the content is less than 3% by mass, the addition amount is insufficient and cracking can not be suppressed. If the content exceeds 13% by mass, the solution is excessively diluted and the coating thickness per one layer becomes thin. And more preferably 6.5% by mass to 10% by mass. If the content is less than 6.5% by mass, cracks are likely to occur. If the content is more than 10% by mass, there is a problem that the thickness of the coating film per one layer is reduced.

A method of preparing a raw material liquid for a PZT sol-gel solution containing a PZT-based compound will be described in accordance with the above-mentioned basic inclusion and the above-mentioned prescription.

The preparation of the raw material liquid for the PZT sol gel liquid is based on the following liquid synthesis flow. First, a Zr raw material, a Ti raw material, and a stabilizer are placed in a reaction vessel and refluxed in a nitrogen atmosphere. Then, a Pb raw material is added to the refluxed compound, and a solvent is added, refluxing in a nitrogen atmosphere, and distillation under reduced pressure to remove by-products. Propylene glycol is further added to the solution to adjust the concentration, Again add ethanol to this solution. More typically, Pb (CH ₃ COO) ₃ ) 3H ₂ O and Zr (Oi-O) are added so that the composition ratio Pb / Zr / Ti of the PZT compound is 115/52/48 (17 mass% Pr) ₄ , and Ti (Oi-Pr) ₄ are weighed to a predetermined weight, and they are dissolved in a solvent such as ethanol to obtain a raw material solution. If necessary, a stabilizer is added to the raw material solution, which will be described below.

The composition ratio Pb / Zr / Ti of the PZT compound can be appropriately changed according to the composition of the desired PZT compound.

Next, addition and mixing of the additives contained in the raw material solution will be described.

In the PZT sol-gel solution according to the present embodiment, the viscosity adjusting polymer compound containing polyvinylpyrrolidone such that the molar ratio of PZT: polyvinylpyrrolidone in terms of monomer is 1: 0.1 to 0.5, Lt; / RTI > The basis of the molar ratio is as described above. After polyvinylpyrrolidone is added to the raw material solution at the above-mentioned molar ratio, the solution is stirred at room temperature for 24 hours. Then, N-methylpyrrolidone is added so as to have a concentration of 3% by mass to 13% by mass of the PZT-based sol-gel solution, stirred for 2 hours, and stabilized at room temperature for 24 hours.

The stabilizer to be contained and the solvent to be used are as follows. In this PZT-based sol gel liquid, if necessary, a stabilizer such as? -Diketones (e.g., acetyl acetone, heptafluorobutanoyl pivaloyl methane, dipivaloyl methane, trifluoroacetylacetone, benzoyl acetone, (for example, lower alkyl esters such as methyl, propyl, butyl and the like of the above-mentioned ketonic acid),? -ketoamides (for example, (E.g., lactic acid, glycolic acid,? -Oxybutyric acid, salicylic acid, etc.), lower alkyl esters of the above oxyacids, oxyketones (e.g., diacetone alcohol, acetone, etc.) (Number of stabilizing agent molecules) / (number of metal atoms) may be added in an amount of 0.2 to 3 equivalents based on the total weight of the composition of the present invention.

The solvent to be used in the present embodiment may be ethanol, but is appropriately determined depending on the raw material to be used. Generally, a carboxylic acid, an alcohol (e.g., propylene glycol as a polyhydric alcohol), an ester, a ketone (e.g. acetone, methyl ethyl ketone), an ether (e.g., dimethyl ether, diethyl ether) , Aromatic hydrocarbons (e.g., benzene, toluene, xylene), and other tetrahydrofuran, or a mixed solvent of two or more of these solvents can be used .

The solvent can be added in an amount of 50 to 70% by mass, more preferably 60 to 65% by mass, based on 100% by mass of the PZT-based sol-gel solution.

Specific examples of the carboxylic acid include n-butyric acid, alpha -methylbutyric acid, i-valeric acid, 2-ethylbutyric acid, 2,2-dimethylbutyric acid, 3,3-dimethylbutyric acid, 3-methylpentanoic acid, 2-ethylpentanoic acid, 3-ethylpentanoic acid, 2,2-dimethylpentanoic acid, 3,3-dimethylpentanoic acid, 2,3- Ethylhexanoic acid, and 3-ethylhexanoic acid are preferably used.

Examples of the ester include ethyl acetate, propyl acetate, n-butyl acetate, sec-butyl acetate, tert-butyl acetate, isobutyl acetate, n-amyl acetate, sec-amyl acetate, It is preferable to use wheat. Examples of the alcohol include aliphatic alcohols such as 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, It is preferable to use 2-methoxyethanol.

The PZT sol gel liquid may contain β-diketones and polyhydric alcohols in an amount of 10 to 20 mass% in 100 mass% of the PZT sol-gel solution. Of these, acetylacetone is preferable as the? -Diketones, and propylene glycol is particularly preferable as the polyhydric alcohols.

The PZT sol-gel solution prepared as described above is applied on a substrate by using a CSD (Chemical Solution Deposition) method such as a spin coating method, a dip coating method, a LSMCD (Liquid Source Misted Chemical Deposition) method, The residual solvent or water is removed to form a gel film, which is then calcined and fired to produce a PZT ferroelectric thin film.

According to the above-mentioned PZT sol-gel solution of the present embodiment, since the viscosity can be increased by adding the polymer and the crack can be suppressed by adding N-methylpyrrolidone, the spin coat 1 A relatively thick film having a thickness of 100 nm or more can be formed in one layer by sintering, and the PZT film after the calcination and sintering is cracked and dense, and sufficiently high ferroelectric characteristics can be obtained, so that the production efficiency can be improved.

Example

Next, examples of the present invention will be described in detail with reference to comparative examples.

Comparative tests and evaluations were as follows.

With respect to the PZT films obtained in Examples 1 to 6 and Comparative Examples 1 and 2, the layer thickness and the refractive index after sintering of the thin film were determined by the following procedure. The results are shown in Table 1. In addition, the cross section and the surface of the PZT film obtained in Examples 1 and 4 and Comparative Example 2 were observed.

(1) Layer thickness measurement: The layer thickness of the obtained PZT film was measured by a spectroscopic ellipsometer (M-2000, manufactured by J. A. Woollam), and the measurement results are summarized in Table 1.

(2) Measurement of refractive index: The refractive index of the PZT film was measured by the spectroscopic ellipsometer, and the measurement results are summarized in Table 1.

(3) Cross-section observation: The cross-section of the obtained PZT film was observed with a photograph (magnification: 100000) photographed by SEM (Hitachi, S-4300SE)

(4) Observation of the surface: The surface of the obtained PZT film was observed with a photograph (magnification: 25000 times) taken by SEM (S-4300SE, manufactured by Hitachi, Ltd.)

≪ Example 1 >

0.73 g of polyvinylpyrrolidone (hereinafter referred to as PVP) (k = 30) as PZT: PVP = 1: 0.2 was added to 50 g of a PZT sol-gel solution of an ethanol solvent containing 25 wt% of PZT as an oxide, The mixture was stirred for 2 hours and stabilized in a refrigerator (5 ° C) for 24 hours. To the thus obtained solution, N-methylpyrrolidone was added in an amount of 6.5% by mass of the solution, and the mixture was stirred for 2 hours. The obtained solution was dropped onto a Pt film of a substrate (hereinafter referred to as " Pt / TiO _x / SiO ₂ / Si substrate ") having an SiO ₂ film, a TiO ₂ film and a Pt film formed in this order on a Si substrate, Spin coating was performed for 60 seconds. The substrate was held on a hot plate at 150 캜 for 3 minutes to remove residual solvent and water in the film. The obtained substrate was subjected to RTA (Rapid Thermal Annealing) process. The temperature was raised to 275 ° C at 2.5 ° C / sec, held for 3 minutes, raised to 460 ° C at 10 ° C / sec and held for 8 minutes.

The refractive index at 632.8 nm of the obtained film was measured to be 2.40. This substrate was baked by RTA treatment at a heating rate of 10 占 폚 / sec and at 700 占 폚 for 1 minute. The refractive index of the obtained PZT film was 2.52. A Pt upper electrode (200 nm) was formed on the obtained PZT film by sputtering, and the electric characteristics were measured. As a result, it was confirmed that the dielectric constant at 0 V was 1500, indicating a high dielectric constant. From the observation by SEM, a dense PZT film with a film thickness of 250 nm was not cracked.

≪ Example 2 >

PVP (k = 30) and 0.91 g of PZT: PVP = 1: 0.25 were added to 50 g of a PZT sol-gel solution of an ethanol solvent containing 25 wt% of PZT as an oxide and stirred for 2 hours, Lt; / RTI > for 24 hours. N-methylpyrrolidone was added to the solution so obtained so as to be 3.0% by mass of the solution, and the mixture was stirred for 2 hours. The obtained solution was dropped onto the Pt film, and spin-coated at 2000 rpm for 60 seconds. The substrate was held on a hot plate at 150 캜 for 3 minutes to remove residual solvent and water in the film. The obtained substrate was subjected to RTA treatment. The temperature was raised to 275 ° C at 2.5 ° C / sec, held for 3 minutes, raised to 460 ° C at 10 ° C / sec and held for 8 minutes.

The refractive index at 632.8 nm of the obtained PZT film was measured to be 2.40. This substrate was baked by RTA treatment at a heating rate of 10 占 폚 / sec and at 700 占 폚 for 1 minute. The refractive index of the obtained PZT film was measured to be 2.50. A Pt upper electrode (200 nm) was formed on the obtained PZT film by sputtering, and the electrical characteristics were measured. As a result, it was confirmed that the dielectric constant at 0 V was 1430 and a high dielectric constant was obtained. From the observation by SEM, cracks did not occur in the PZT film having a dense columnar structure with a film thickness of 280 nm.

≪ Example 3 >

1.64 g of PVP (k = 30) was added to 50 g of a PZT sol-gel solution of an ethanol solvent containing 25 wt% of PZT as an oxide and PZT: PVP = 1: 0.45. The mixture was stirred for 2 hours, Lt; / RTI > for 24 hours. N-methylpyrrolidone was added to the solution so obtained so as to be 3.0% by mass of the solution, and the mixture was stirred for 2 hours. The obtained solution was dropped onto the Pt film, and spin-coated at 2000 rpm for 60 seconds. The substrate was held on a hot plate at 150 캜 for 3 minutes to remove residual solvent and water in the film. The obtained substrate was subjected to RTA treatment. The temperature was raised to 275 ° C at 2.5 ° C / sec, held for 3 minutes, raised to 460 ° C at 10 ° C / sec and held for 8 minutes.

The refractive index of the obtained PZT film at 632.8 nm was 2.40. This substrate was baked by RTA treatment at a heating rate of 10 占 폚 / sec and at 700 占 폚 for 1 minute. The refractive index of the obtained PZT film was measured to be 2.50. A Pt upper electrode (200 nm) was formed on the obtained PZT film by sputtering, and the electric characteristics were measured. As a result, it was confirmed that the dielectric constant at 0 V was 1430 and the dielectric constant was sufficiently high. Further, from the observation by SEM, a dense PZT film with a film thickness of 350 nm was not cracked.

<Example 4>

1.64 g of PVP (k = 30) was added to 50 g of a PZT sol-gel solution of an ethanol solvent containing 25 wt% of PZT as an oxide and PZT: PVP = 1: 0.45. The mixture was stirred for 2 hours, Lt; / RTI &gt; for 24 hours. To the thus obtained solution, N-methylpyrrolidone was added in an amount of 6.5% by mass of the solution, and the mixture was stirred for 2 hours. The obtained solution was dropped onto the Pt film, and spin-coated at 2000 rpm for 60 seconds. The substrate was held on a hot plate at 150 캜 for 3 minutes to remove residual solvent and water in the film. The obtained substrate was subjected to RTA treatment. The temperature was raised to 275 ° C at 2.5 ° C / sec, held for 3 minutes, raised to 460 ° C at 10 ° C / sec and held for 8 minutes.

The refractive index of the obtained PZT film at 632.8 nm was 2.41. This substrate was baked by RTA treatment at a heating rate of 10 占 폚 / sec and at 700 占 폚 for 1 minute. The refractive index of the obtained PZT film was 2.51. A Pt upper electrode (200 nm) was formed on the obtained PZT film by sputtering, and the electric characteristics were measured. As a result, it was confirmed that the dielectric constant at 0 V was 1450 and the dielectric constant was sufficiently high. Also, from the observation by SEM, a highly dense PZT film having a film thickness of 320 nm was not cracked.

&Lt; Example 5 &gt;

1.64 g of PVP (k = 30) was added to 50 g of a PZT sol-gel solution of an ethanol solvent containing 25 wt% of PZT as an oxide and PZT: PVP = 1: 0.45. The mixture was stirred for 2 hours, Lt; / RTI &gt; for 24 hours. To the thus obtained solution, N-methylpyrrolidone was added in an amount of 13.0% by mass of the solution, followed by stirring for 2 hours. The obtained solution was dropped onto a Pt film, and spin-coated at 2000 rpm for 60 seconds. The substrate was held on a hot plate at 150 캜 for 3 minutes to remove residual solvent and water in the film. The obtained substrate was subjected to RTA treatment. The temperature was raised to 275 ° C at 2.5 ° C / sec, held for 3 minutes, raised to 460 ° C at 10 ° C / sec and held for 8 minutes.

The refractive index of the obtained PZT film at 632.8 nm was 2.42. This substrate was baked by RTA treatment at a heating rate of 10 占 폚 / sec and at 700 占 폚 for 1 minute. The refractive index of the obtained PZT film was measured to be 2.50. A Pt upper electrode (200 nm) was formed on the obtained PZT film by sputtering, and the electric characteristics were measured. As a result, it was confirmed that the dielectric constant at 0 V was 1500 and the dielectric constant was sufficiently high. From the observation by SEM, a dense PZT film with a film thickness of 300 nm did not cause cracking.

&Lt; Example 6 &gt;

1.82 g of PVP (k = 30) and PZT: PVP = 1: 0.5 were added to 50 g of a PZT sol-gel solution of an ethanol solvent containing 25 wt% of PZT as an oxide and stirred for 2 hours, Lt; / RTI &gt; for 24 hours. To the thus obtained solution, N-methylpyrrolidone was added in an amount of 6.5% by mass of the solution, and the mixture was stirred for 2 hours. The obtained solution was dropped onto the Pt film, and spin-coated at 2000 rpm for 60 seconds. The substrate was held on a hot plate at 150 캜 for 3 minutes to remove residual solvent and water in the film. The obtained substrate was subjected to RTA treatment. The temperature was raised to 275 ° C at 2.5 ° C / sec, held for 3 minutes, raised to 460 ° C at 10 ° C / sec and held for 8 minutes.

The refractive index of the obtained PZT film at 632.8 nm was 2.38. This substrate was baked by RTA treatment at a heating rate of 10 占 폚 / sec and at 700 占 폚 for 1 minute. The refractive index of the obtained PZT film was measured to be 2.47. A Pt upper electrode (200 nm) was formed on the obtained PZT film by sputtering, and the electrical characteristics were measured. As a result, it was confirmed that the dielectric constant at 0 V was 1400 and a high dielectric constant was obtained. From the observation by SEM, a dense PZT film having a thickness of 360 nm did not cause cracking.

&Lt; Comparative Example 1 &

PVP (k = 30) and 0.18 g of PZT: PVP = 1: 0.05 were added to 50 g of a PZT sol-gel solution of an ethanol solvent containing 25 wt% of PZT as an oxide and stirred for 2 hours, Lt; / RTI &gt; for 24 hours. To the thus obtained solution, N-methylpyrrolidone was added in an amount of 6.5% by mass of the solution, and the mixture was stirred for 2 hours. The obtained solution was dropped onto the Pt film, and spin-coated at 2000 rpm for 60 seconds. The substrate was held on a hot plate at 150 캜 for 3 minutes to remove residual solvent and water in the film. The obtained substrate was subjected to RTA treatment. The temperature was raised to 275 ° C at 2.5 ° C / sec, held for 3 minutes, raised to 460 ° C at 10 ° C / sec and held for 8 minutes.

The refractive index at 632.8 nm of the obtained PZT film was measured to be 2.40. This substrate was baked by RTA treatment at a heating rate of 10 占 폚 / sec and at 700 占 폚 for 1 minute. The refractive index of the obtained PZT film was measured to be 2.51. A Pt upper electrode (200 nm) was formed on the obtained PZT film by sputtering, and the electric characteristics were measured. As a result, the dielectric constant at 0 V was 1200. From the observation by SEM, the film thickness was 190 nm, and cracks occurred in the film.

&Lt; Comparative Example 2 &

PVP (k = 30) was added to 50 g of a PZT sol-gel solution of an ethanol solvent containing 25 wt% of PZT as an oxide and 2.73 g of PZT: PVP = 1: 0.75 was added and stirred for 2 hours, Lt; / RTI &gt; for 24 hours. To the thus obtained solution, N-methylpyrrolidone was added in an amount of 6.5% by mass of the solution, and the mixture was stirred for 2 hours. The obtained solution was dropped on the Pt film and spin-coated at 2000 rpm for 60 seconds. As a result, the viscosity of the solution was too high to uniformly coat. The substrate was held on a hot plate at 150 캜 for 3 minutes to remove residual solvent and water in the film. The obtained substrate was subjected to RTA treatment. The temperature was raised to 275 ° C at 2.5 ° C / sec, held for 3 minutes, raised to 460 ° C at 10 ° C / sec and held for 8 minutes.

The refractive index of the obtained PZT film at 632.8 nm was 2.05. This substrate was baked by RTA treatment at a heating rate of 10 占 폚 / sec and at 700 占 폚 for 1 minute. The refractive index of the obtained PZT film was measured to be 2.21. A Pt upper electrode (200 nm) was formed on the obtained PZT film by sputtering and the electric characteristics were measured. As a result, the dielectric constant at 0 V was 850. From the observation by SEM, the film thickness was 470 nm and cracks were generated in the film.

<Overall evaluation>

From the above, the PZT films of Examples 1 to 6 relating to the present invention all had better refractive index than the PZT films of Comparative Examples 1 and 2. In addition, the PZT film of the embodiment related to the present invention is a dense film, and cracks did not occur. On the other hand, the PZT film of the comparative example was a film lacking in denseness or cracks. From the above, it was found that the use of the sol-gel solution for forming a ferroelectric thin film of the present invention for the raw material of the PZT film makes it possible to produce a PZT film having a cracked and dense film and having sufficient practical characteristics.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Additions, omissions, substitutions, and other modifications of the configuration are possible without departing from the spirit of the present invention. The invention is not limited by the foregoing description, but is only limited by the scope of the appended claims.

The sol-gel solution for forming a ferroelectric thin film of the present invention can be used for a precursor solution for producing an electronic device or an electronic device including a ferroelectric such as a thin film piezoelectric device or a thin film capacitor in which a relatively thick ferroelectric thin film is required.

Claims (3)

PZT compound,
A viscosity-adjusting polymer compound containing polyvinylpyrrolidone,
An organic dopant containing N-methyl pyrrolidone,
Wherein the PZT-based compound is contained in an amount of at least 17 mass%
Wherein the molar ratio of the polyvinylpyrrolidone to the PZT-based compound is PZT compound: polyvinylpyrrolidone = 1: 0.1 to 0.5 in terms of a monomer,
Wherein the N-methylpyrrolidone is contained in an amount of 3 mass% to 13 mass% of the sol-gel solution. The method according to claim 1,
Wherein the k value of the polyvinylpyrrolidone is in the range of 15 to 90. The ferroelectric thin film forming sol- A method for forming a ferroelectric thin film using the sol-gel solution for forming a ferroelectric thin film according to any one of claims 1 to 3.